Micro Electro-Mechanical System (MEMS) is called Micro-System-Technology in Europe. MEMS is started in combining the semiconductor manufacturing process with the precisely mechanical technology for researching and developing the micro bio-mechanical photoelectric element and the micro system with integrated function. The MEMS is a tiny system with the ability of performing a predetermined action, and its size has become more compact with the improvements of science and technology. A compact system has lots of advantages, such as space-saved, material-saved, low-pollution, and energy-saved. Further, once the relevant technology matures, it would be possible to manufacture the compact system on a large scale economically.
Nowadays, the MEMS is a growing trend for the whole world, but the relevant definitions are not quite the same between different areas, for example it is generally called Micro-System-Technology in Europe but called Micro-Machines in Japan. A general definition of the MEMS is an intelligent tiny system with the capabilities of sensing, processing, actuating and so on. MEMS integrates the properties of electronics, mechanism, optics, chemistry, biology, magnetics or other sciences into a signal or more chips. In the U.S., the MEMS means an integrated micro element or an integrated micro system which includes the electronic and mechanical elements produced by the integrated circuit (IC) compatibility batch processing technology. Further, the size thereof is in the micrometer level to the millimeter level.
In Taiwan, the definition of MEMS includes the definitions of U.S., Europe, and Japan, and it is usually called MEMS technology. The relevant technologies included therein are silicon-based technologies, the LIGA technology, that means the “lithograpie galvanoformung abformung” in German and the lithography electroforming micro molding in English, and other traditional technologies. The LIGA technology includes the technologies of photoetching, electroforming, molding and so on, and can be divided into two parts of laser LIGA and X-ray LIGA. The MEMS is used to manufacture micro sensors, signal processors, micro actuators and so on by applying the system technology, the micro technology, and the material effect technology. The MEMS can be used in various industries, such as the manufacturing industry, the automation industry, the information and transmission industries, the aerospace industry, the traffic transportation industry, the construction industry, the environmental-protection industry, agriculture, the medical equipment industry and so on.
A general MEMS includes a micro sensor, a micro actuator and an integrated circuit, and its main feature is being compact. A compact size makes the MEMS to have some advantages such as being capable to be used in the structure with high precision and high stability, being capable to manufacture lots of identical elements into a tiny area, and being capable of manufacturing the products in batches for saving money and increasing the production efficiency. To sum up the above, the advantages of the MEMS are space-saving, money-saving, highly competitive due to its compact size.
Three main semiconductor manufacturing processes are the thin film growing, the photolithography, and the etching. However, the MEMS manufacturing process is based on and extended from the present semiconductor manufacturing processes. Further, the manufacturing process of MEMS is more flexible and variable than that of a general IC. For example, the MEMS manufacturing process includes the thin film growing, the photolithography, the wet etching, the dry etching, the anisotropic etching, the electroform, the silicon micromachining, and so on. In which, the silicon micromachining includes the bulk micromachining, the surface micromachining, and the LIGA technology.
1. Bulk micromachining: A bulk micromachining is a processing technology that uses a silicon chip as the base material for etching and segmenting. Since the commonly used materials are silicon chips and glasses, the micromachining process has some limitations, i.e. it has a bonding temperature limitation during a doping process therein, and it has an electric field limitation for a base material having electric circuits located thereon. In addition, it is common to accelerate the micromachining and increase the boding strength by increasing the processing temperature. However, since the expanding factors of various materials are different from each other, once the processing temperature cools down, a thermal stress occurs between the materials and leads to some breakages. In the other words the yields of the manufactured elements will be reduced. In addition, since some elements are specific in purpose use, they have the limitations about the base materials. For example, an insulating material, such as a glass, is essential for manufacturing an electrophoresis chip. Furthermore, the bulk micromachining usually includes an etching process, preferably a wet etching. The chip for bulk micromachining usually has a size from several millimeters to micrometers and the etching depths into the chip are from millimeters to micrometers.
2. Surface micromachining: A surface micromachining is similar to the traditional IC semiconductor manufacturing process. In tradition, a semiconductor component is formed by stacking multiple thin layers together via the processes of evaporation, sputtering or chemical deposition. Since every micromechanical structure of the component is formed by depositing thin films, the precision and the resolution of the component manufactured by the surface micromachining are better than those manufactured by the bulk micromachining. Therefore, while processing a one-chip circuit, a microstructure or a micro sensor, the surface micromachining is more advantageous than the bulk micromachining. However, for manufacturing a MEMS component, the two micromachinings are incomparable with each other, since it depends on the desirous property and the function of the component.
3. LIGA process: The LIGA process is a technology from Germany and its original text is “lithographic galvanoformung abformung”, which is called as LIGA for short. The LIGA process includes the technologies related to the optics, electroplating, and modeling. The LIGA process is an optical etching mainly using an X-ray as its light source. During the LIGA process, some patterned masks or photoresist (for example, the polymethyl methacrylate PMMA) are used to selectively covers some surfaces of the substrate, and then the exposed parts are etched by various light. After etched, the substrate is electroformed and processed with an injection-modeling so as to form the desirous product. Further, the application fields of the LIGA process are wider than those of bulk micromachining and surface micromachining.
In addition, since the MEMS also includes the micro-manufacturing technology, the bonding technology, the packaging technology, and the checking technology, the MEMS is also called micro-system basic technology.
In the past, during the process of manufacturing an element via the traditional bulk micromachining of the MEMS, different parts of the element are made from different silicon chips. After manufactured, the different parts are combined together and formed the element via a micro-assembling technology. That is to say the MEMS element is formed from different components manufactured independently. However, since the thicknesses of the different silicon chips are different from each other, to assemble them is quite difficult. In order to solve the above problem, it is desirable to manufacture the different parts of an element from a single one silicon chip is desirable. In addition, to manufacture an element via a MEMS surface micromachining is limited by the thicknesses of the deposition materials and the internal stresses formed during the deposition process, so that it is difficult to manufacture an element with wide area, high flatness, and great displacement via a MEMS surface micromachining. Therefore, it is also desirable to manufacture an element via a MEMS bulk micromachining.